Hydrophilic vegetable gums have been known and utilized for a variety of industrial applications for many years. They are readily utilized in aqueous solutions in many manufacturing processes such as textile, cosmetic, foodstuff, and the drilling and secondary production of subterranean wells. Of particular importance is their ability to form viscous colloidal dispersions in aqueous environments.
Even in small quantities, the addition of the gum causes an increase in viscosity and in some instances a gel structure develops. This gel formation is especially desirable when minute undissolved solids are present in an environment, and must be maintained in a relatively uniform state of dispersion after agitation has been reduced or terminated. Such conditions are typical in the drilling of subterranean wells for oil, gas, water, and the like. One of the most versatile hydrophilic vegetable gums is galactomannan gum, which has a high tolerance for the presence of electrolytes.
To enhance thixotropic characteristics and enable greater viscosities to be developed from a given amount of the galactomannan material in solution, a crosslinking effect may be utilized. Linear polymer chains can be joined together by materials having two or more functional groups. The crosslinking may involve covalent, ionic-coordination or hydrogen bonds. Weaker bonding, such as achieved through hydrogen bonding, induces a labile structure that is easily disrupted by mechanical force.
The polygalactomannan gums are polysaccharides composed principally of galactose and mannose units and are usually found in the endosperm of leguminous seeds, such as guar, locust bean, honey locust, flame tree, and the like. Guar flour, for example, is composed mostly of a galactomannan which is essentially a straight chain mannan with single membered galactose branches. The mannose units are linked in a 1-4-.beta.-glycosidic linkage and the galactose branching takes place by means of a 1-6 linkage on alternate mannose units. The ratio of galactose to mannose in the guar polymer is, therefore, one to two. Guar gum has a molecular weight of about 220,000.
Locust bean gum is also a polygalactomannan gum of similar molecular structure in which the ratio of galactose to mannose is one to four. Guar and locust bean gum are the preferred sources of the polygalactomannans, principally because of the commercial availability thereof.
Polygalactomannan gums swell readily in cold water and can be dissolved in hot water to yield solutions which characteristically have a high viscosity even at a concentration of 1-1.5 percent. Guar gum and locust bean gum as supplied commercially usually have a viscosity (at 1% concentration) of around 1000 to 4000 centipoises at 25.degree. C. using a Brookfield Viscometer Model LVF, spindle No. 2 at 6 rpm.
There are various rigorous applications that require greater stability under variable conditions than is provided by hydrocolloid gums that are commercially available. For example, it is desirable that a gum which functions as a protective colloid or gelling agent in oil well drilling mud compositions and oil well fracturing compositions exhibit a degree of solution stability and heat stability under operating conditions.
Further, solutions of ordinary hydrocolloid gums are not sufficiently stable under variable conditions of pH and temperature, or not sufficiently stable in the presence of polyvalent metal ions, to qualify for general application in the textile industry for sizing, printing and finishing operations, or in the paper industry as sizing and coatings agents.
Accordingly, it is a main object of the present invention to provide hydrocolloid gum compositions having improved viscosity properties for applications in petroleum, textile, printing, paper and pharmaceutical industries.
It is another object of the present invention to provide dry blends of polygalactomannan gum-containing thickening compositions and high viscosity aqueous solutions produced therewith.
It is a further object of the present invention to provide thickening agents which have superior solution stability and heat stability, and which contribute exceptionally high viscosity to aqueous solutions due to a synergistic viscosity effect derived from the interaction of thickening agent components.
Other objects and advantages shall become apparent from the following description and examples.